Polyvinyl alcohol photographic silver halide emulsions



United States Patent 3,113,025 POLYVINYL ALQGHQL PHGTOGRAPHEC @llLVER HALHDE EMULSiONS Joseph A. Sprung, Binghamton, NY, assignor to General Aniline & Film Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed fan. 19, 1959*, leer. No. 787,353:

28 Clm'ms. (G. 96-1ti7) This invention relates to photographic silver halide emulsions which comprise a silver halide dispersed in a polyvinyl alcohol polymer carrier and to photographic layers produced therefrom. More particularly, it rela es to the control of the photographic properties of such silver halide polyvinyl alcohol emulsions by the use of various surface-active agents designated hereafter as photographic activators or sensitizers.

It has long been the goal of the photographic industry to replace gelatin with a more satisfactory carrying vehicle for the light-sensitive silver halide salts in photographic emulsions. Perhaps the main objection to the use of gelatin can be attributed to the fact that it is a natural product and, therefore, is subject to variations in composition which may cause difficulties in controlling the photographic properties of the emulsions prepared therefrom. For instance, each batch of fresh gelatin must ordinarily be submitted to a wide variety of tests, including the preparation of sample emulsions, to determine its photographic activity before it can be accepted for manufacturing use. In addition, photographic emulsions based on gelatin are brittle, subject to attack by bacteria and fungi and cannot be processed at elevated temperatures without special prior treatment. Despite the serious drawbacks, gelatin still remains the standard silver halide carrier in practically all commercial photographic emulsions. Its general acceptance, notwithstanding its many disadvantages, stems from the fact that it possesses a number of unique physical and chemical properties which make it ideal for photographic applications.

Gelatin is a thermo-reversible substance, and because of this property, the production of photographic emulsions prepared therefrom is greatly facilitated. The emulsions can be chilled to produce solid gels which can be subsequently shred into particles and readily washed free of unwanted soluble salts by simple washing procedures. The thermo-reversibility of gelatin is also highly inst-rumental in facilitating the coating operation of photographic emulsions since setting of the liquid emulsion occurs immediately on contact with a chilled base.

Gelatin also functions as a peptizing agent for the insoluble silver salts, and provides the essential sensitizing and restraining principles which govern the light-sensitive characteristics of the silver halide grains.

The light-sensitivity of a gelatin silver halide photographic ernulsion is determined mainly by: (1) the size and distribution of the silver halide grains and (2) the acquisition from the gelatin of certain sulfur chemical sensitizing constituents. The crystal growth in an emulsion is usually referred to as physical or Ostwald ripening, While the action of the sulfur sensitizers on the grains is known as chemical sensitization. By properly controlling the size and distribution and the chemical sensitization of the silver halide grains, photographic emulsions, having a wide variety of characteristics and applications, can be produced. l

Various synthetic materials have been proposed as substitutes for gelatin but none, except possibly polyvinyl alcohol, has shown much promise as being able to satisfy the exacting photographic requirements.

Some of the desirable physical properties of polyvinyl alcohol which qualify it as a carrier for the silver halide salts in photographic emulsions are: (1) it is capable of ice suspending silver halide grains; (2) the polyvinyl alcohol emulsions can be washed by dialysis, or can be precipitated and washed by decantation to remove the soluble salts; (3) the emulsions can be coated on paper or a suitable subbed film base; and (4) the coated emulsions can be hardened and processed in the conventional developing and fixing solutions.

While polyvinyl alcohol is acceptable mechanically as a silver halide carrying vehicle, it, nevertheless, lacks some of the physical and chemical features of gelatin which facilitate the preparation of photographic emulsions, pa icularly those in the high speed range. Pure polyvinyl alcohol, unlike gelatin, is highly restraining and does not permit the growth (Ostwald ripening) of the silver halide grains. In addition, unmodified polyvinyl alcohol silver halide emulsions cannot be ripened chemically to increased light-sensitivity with the conventional labile sulfur compounds known to be eiiective in the gelatin emulsion system. Since emulsion speed is dependent upon the attainment of proper grain size and response to chemical sensitization, it is apparent why polyvinyl alco hol has been used in the past only for the preparation of low speed contact printing papers.

It has now been discovered that the photographic properties of non-gelatin silver halide emulsions can be regulated or controlled by adjusting the surface charge on the silver halide grains by means of selected surface-active agents. The method of preparing such photographic emulsions constitutes an important object of this invention.

it is a further object of this invention to provide a polyvinyl alcohol silver halide photographic emulsion having surface-active agents incorporated therein to render it capable of grain growth (physical ripening) and chemical sensitization in the [manner of the conventional gelatin emulsions.

It is a further object of this invention to provide a method for increasing the silver halide carrying capacity of polyvinyl alcohol.

It is a further object of this invention to provide polyvinyl alcohol silver halide emulsions which will respond to optical sensitization in the manner of the conventional gelatin emulsions.

A still further object is to provide a process of prepar ing polyvinyl alcohol silver halide photographic emulsions and emulsion layers therefrom which are equal in light-sensitivity to commercially available photographic materials.

Other objects will appear hereinafter as the description proceeds.

According to the present invention, polyvinyl alcohol silver halide emulsions of predetermined and predictable photographic characteristics can be produced by cont-rolling the electrical charge pattern on the surface of the silver halide grains. Such a charge pattern is established by surrounding the light-sensitive grains with certain surface-active materials or activators which are adsorbed on the silver halide crystal surface. I have found that the desired electrical charge pattern can be achieved by preparing polyvinyl alcohol photographic emulsions in the presence of various surface-active ampholytic or combinations of surface-active ampholytic and cationic agents.

The surface-active substances which are useful for this invention are characterized by possessing an aliphatic chain of at least 8 carbon atoms which is linked to an anionic and/or cationic functional group. In the case of the cationic surfaceactive agents, the functional group may be represented by primary amino (NH secondary amino NH), tertiary amino 3 quaternary ammonium N+ hydrazino (-NH-NH azonium (NIIN+:

guanyl N112 guanido NH NIIO\ N11 biguanido (NII-(flJ-NH-fi-Nflz) NH NII amine oxide ternary sulfonium or quaternary phosphonium Substltuents.

Such surface-active cationic agents impart a positive charge on the silver halide grain surface to which they become adsorbed. By appropriate modifications in the chemical make-up of the cationic agents, the intensity of the positive charge can be varied. Since the photographic activity of the light-sensitive grains is closely associated with the nature of the positive charge, the structure of the cationics can be altered to produce silver halide emulsions having a variety of photographic proper-ties.

However, silver halide emulsions sensitized with surface-active cationics tend to be foggy, a condition that calls for rather large quantities of stabilizers. As a consequence, the emulsions are slow and useful only for such limited applications as printing paper.

I have now found that the introduction of certain negative or acidic substituents into the cationic molecule gives rise to a sensitizer having greatly improved photographic properties compared to the unmodified cationic structure. The resulting entities, since they are characterized by residual positive and negative charges, are amphoteric in nature.

Typical of the acidic or negative substituents, which can be employed as modifiers in the manner described above, include: carboxylic acid (COOH), sulfonic acid (SO H), sulfinic acid (SO H), sulfuric ester (OSO H) phosphonic acid (PO H phosphonous acid 2 2) phosphoric monoester (OPO H phosphoric diester mercapto (SH), or phenolic hydroxy (OH) groups.

Since these amphoteric substances, sometimes referred to herein as ampholytes, contain both cationic and anionic substituents, they may be represented by the inner salt or zwitterion formula or they may be written as acid, basic or neutral salts. The particular form assumed by the ampholytes depends on their mode of preparation and on the pH of the surrounding medium.

A. The various forms may be represented as follows:

wherein F+ represents an onium grouping, An represents an acidic substituent of the type above, Q represents a divalent organic grouping containing an aliphatic chain of at least 8 carbon atoms, X represents an anion, M represents ammonium or an alkali metal, and H is hydrogen.

While many compounds embraced by the above formulae are suitable for my purpose, I normally employ those of the following formulae:

wherein F+ represents an ammonium group, Q represents a divalent organic grouping such as a chain comprising carbon, nitrogen, oxygen, sulfur or aryl rings of the henzene and naphthalene series, X represents an anion, M represents ammonium or alkali metal, and H is hydrogen.

Compounds falling within the ambit of the Formula I include aminocarboxylic acids, betaines, taurines and thetaines, said compounds having an aliphatic chain of at least 8 carbon atoms.

Illustrative of the surface-active materials of the type described above are compounds represented by the following formulae:

CATIONICS wherein Alk represents an aliphatic chain of at least 8 carbon atoms and B represents hydrogen, carbloweralkyl, carboxamido or amino groups.

H A1kNR1 wherein Alk has the Value given above and R represents a lower alkyl group.

wherein R and R represent lower alkyl groups or together can form a heterocyclic ring system of the pyrrolidine series, piperidine series, pyridine series, morpholine series or quinoline series, Alk has the value given above and can be substituted by an amino group and F represents an intermediate linkage such as a carbon atom or grouping such as NH--CO (CH wherein n is an integer of from 1 to 4; -NHSNH-CO(CH wherein S can be a lower alkylaryl bridge of the benzene and naphthalene series and n has the value given above; CONH-(CH wherein n has the value given above; -ArylOCH .CI-I OCH .CH wherein m is an integer of from 1 to 3 and Aryl is an aryl group of the benzene and naphthalene series.

H AlkC ONR4 wherein Alk has the value given above and R is a heterocyclic ring system such as pyridine, quinoline and benzothlazole and the quaternary salts thereof.

NH NH H% and Alk-YN NHz and

AlkYNH-CNHCNH2.2HX

NH I IH wherein Alk, X and Y have the values given above.

3/ AlkU R1 wherein R and Alk havthe value given above; R represents lower alkyl which can be substituted by aryl groups of the benzene and naphthalene series, carbamyl groups, lower alkoxyl carbonyl groups, 2-succimidyl groups, lower alkylamido groups, acyl groups and heterocyclic nuclei of the pyridine, quinoline and benzothiazole series; U represents a single carbon-nitrogen linkage, a bridge such as -Aryl-OCH .SH (OCH .CH wherein m is an integer of from 1 to 3 and Aryl represents an aryl group of the benzene and naphthalene series, a bridge such as -CONH(CH wherein n has value given above, CONHCH .CONH(CH ),,wherein n has the value given above, -succimido lower alkyl, -NHCO(CH wherein n has the value given above, -o-Aryl-CONH(CH wherein Aryl and n have the values given above,

CONH-Aryl-CONH (CH wherein Aryl and n have the values given above and X has the value given above.

ii. wherein R represents hydrogen or lower alkyl; R represents an alkyl group which can be directly linked to the heterocyclic nucleus or through a CONH-- bridge; and R represents an alkyl group which can be substituted by aryl radicals of the benzene and naphthalene series, carbamyl radicals and carbloweralkoxyl radicals, and one of said R and R always containing an alkyl group of at least 8 carbon atoms, V represents the non-metallic atoms necessary to complete a heterocyclic nucleus of the benzothiazole series, pyridine series, quinoline series and benzirnidazole series and X has the value given above.

CONH-Arylene-CONH- wherein Arylene is a mono or bicyclic aromatic radical, -o-Arylene-CO-- wherein Arylene has the values given above --CONH-(CH wherein n has the value given above and -SO and X has the value given above.

wherein Alk, R and X have the values given above.

wherein Alk, R and X have the values given above.

As previously pointed out, the photographic properties of a silver halide polyvinyl alcohol emulsion can be regulated by adjusting the electrical charge at or near the silver halide grains. Such a charge can be established by the adsorption of various surface-active agents at the silver halide surface. Although the aforesaid cationics make it possible to establish a positive charge of varying intensity around the light-sensitive silver halide grains, precise control of the photographic properties of the emulsion necessitates adjusting the negative charge as well. Thus, by the introduction into the cationic molecule of the various acidic groups of the type illustrated above, a structure is thereby produced having positive and negative seats or charges. By selecting the proper combination of negative and positive groupings, an amphoteric compound or ampholyte can be produced capable of controlling the charge pattern and, therefore, the photographic properties of a polyvinyl alcohol silver halide emulsion with much greater precision than by means of the cationics alone.

In the following list are depicted various ampholytes which are illustrative of the types used in accordance with this invention.

Aliphatic amino carboxylic acids and taurines having an alkyl radical of at least 8 carbon atoms.

Betaines of the formula:

wherein R and R have the values given above; K can be single carboncarbon bond, a polymethylene bridge of from 1 to 4 carbon atoms, a linkage such as wherein t is an integer of from 1 t0 4 wherein it has the value given above,

Alk

| CH2.COOH

wherein Alk has the value given above, CONl-I-Aryl-- wherein Aryl has the value given above, CH --o-Aryl wherein Aryl has the value given above, -CO-Aryl wherein Aryl has the value given above; R and R represent hydrogen, alkyl, one of which can be substituted by an amino group; and R and R together can complete a heterocyclic nucleus of the pyridine series; R can be an alkyl group attached directly to the quaternary nitrogen atom or through an intervening linkage (L) of the type described above for U under aliphatic quaternary ammonium compounds and one of R R and R always being an alkyl chain of at least 8 carbon atoms, T is an acid radical such as --COOH,. --SO H, or PO H and X has the value given above.

Thetines of the formula:

Alk-S-(OHQr-T wherein Alk, R T and n have the values given above.

wherein R Alk and n have the values given above.

All of the ampholytic and cationic materials, of the type used herein, are provided with long chain or polymeric moieties to endow the molecules with surface-active properties which greatly influence their mode of adsorption on the silver halide grains. According to the photographic literature, such surface-active agentsare capable of displacing simple ions (e.g., Ag or Br) from the silver halide grain surface.

By properly selecting and applying the appropriate surface-active ampholytes or combinations of ampholytes and cationics, it is possible to control the type, number and distribution of charged sites on the silver halide grain surface.

The establishment of a predetermined charge arrangement on or about the silver halide grain not only facilitates grain growth and peptization, but regulates the subsequent adsorption of photographically active ions (sulfur sensitizers, gold sensitizers, stabilizers and developers, etc.) all of which have a profound influence on the photographic characteristics of the ripened, exposed and processed emulsions. Although such compounds possess similar cationic and anionic functional groups, the various auxiliary substituents, depending on their position in the molecule, markedly influence the degree of adsorption of the surface-active materials on the silver halide grain and thereby affect the physical and chemical ripening properties of the photographic emulsions prepared therefrom.

The application of the appropriate materials permits the preparation of polyvinyl alcohol emulsions possessing a selected range of grain sizes and therefore exhibiting a wide variety of speed and gradation characteristics.

In general, it has been observed that the surface active cationics are difficult to apply because of their fogging tendencies, and can only be used for the preparation of low speed paper emulsions which are highly stabilized with synthetic antifoggants. The surface-active ampholytes, on the other hand, permit the greatest latitude in emulsion-making conditions, and can be applied over a wide concentration range without producing an undesirable fog level. In some instances, as will be described later, the ampholytes are advantageously used in combination with the cationics in order to bring out their maximum peptizing and sensitizing properties.

The following is a detailed list of the various activators which are useful in the preparation of the polyvinyl alcohol photographic silver halide emulsions described herein. In all the compounds, the chemical structure of each contains a polymeric moiety or an alkyl or alkylene chain of at least 8 carbon atoms.

Table I SURFACE-ACTIVE CATIONIC AGENTS Compound N0. Structure (0 =cationic) CH3 C-3 C 4H29N CH3 0-4 C H33N CH (3-5 C1 H37N CH3 C-G CgHu-O-O CHzCHzO CH2CHZN C-7 HzNCH2CHz(OH2)1o-CH2CH2N z CHzCH2 CHzCHz C-S O N(CHz)1oN O CH2CH2 CHzCHg 0-9 N(CH2)in-N C4119 CzH 0-10 N-(CH2)ro-N C4H9 CgHg, 0-11 cmnu-oHc o 0 02115. H01

0-12 C1DH CHC ONHz.HCl

CH 0-13 G1uH ;NHC o CHPN C-14 CmHaaNH-C O CH2N Table I--Continued SURFACE-ACTIVE CATIONIC AGENTS Compound N0. Structure (0 =cationic) /0 Ha 0-15 0711150 ONH(CH3)3N\ CH3 0-15 CnHmC ONH(CH2)3N\ CH3 C-l 01111230 0 NH-(CHMN CHa C-lS 01311270 ONH-(CH2)3N CH3 C-19 015E316 ONH-(CHahN CH: 0-20 C17Hsa C O NH-(CHz) 3N 0-21 14H2eNH-CHz-C /CH3 0-22 (CHz)a CONH(CH2)a-N CgH5 0-23 CnHasC ONH-(CHflr-N CgHg C-24 61313270 0 NH- L NHC 0 0131127 0-26 CH-CHg w A L NH 0-27 CsH17NH-C .HX

C28 CmHnNH-C .HX

NH C29 CnHzsNH-C .HX

NH 0-30 CmHznNH-C LHX NH 0-31 C|aHa3NHC .HX

Table I-Continued SURFACE-ACTIVE OATIONIC AGENTS Compound No. (G= Structure cationic) 5 0-65 CmH33OC -C ONH(CH2)aIII+GHa X- CH; C 1 0-66 C15H31CONH- CONH(CHZ)3III CH3 X- CH (IJHa (1-67 0 5E 0 ONH- C ONH-(CH2)a1;T CH3 X- CmHas mHav 0-70 C1uHz -(lJH-C ONE: X

0-71 0-0 ONHOBHU X- 0-74 L CmHaa X 0-75 C ONHCmHaa X" C-76 ONHCmHa; X

Table lCo11tinued SURFACE-ACTIVE OATIONIO AGENTS Compound No. (C= Structure cationic) 0-77 COOC2H X- 0-78 (CHCH- r X- A Lm hHe C-CHa X- uaHav CH3 0-80 C12H25II\T+-NHZ X CH3 CSI C1aH33l I*NHg X- CH3 0-82 OISH37I I -NHQ X- CH: 0-83 CHaC O NH-I I CmH33 X" CHa 0-84 01 E310 ONHl I CHa X- CH C-85 0 1E3 0 ONH-I I+CH X- C-86 01511310 ONHN -CHzC O 0 CzH X- CH 0-87 01511310 ONHQ-CONH-I'W-GH X- CH C ONH-1 I+-CH X- CH \i 0-89 C1uHa3N -C 3 8 0-90 C17Ha5CONH(CH2)3-1 T+- X- Table IContinued SURFACE-ACTIVE CATONIG AGENTS Compound No. (0: Structure cationic) -91 C1uHaa ;;I3 N X CI-I (3-92 0 113 8 0 zNHl I CHa X- CH3 0-93 C 4Hg9 CzH5 X C-94 C1511333OZNH-(CH2)3N+CH3 X" CH 0-95 01111230 0 NHS O zNI-I (CH2) I I CHQ X" Table 11 Compound N o. (A ampholyte) SURFACE-ACTIVE AMPHOLYTIO AGENTS Structure m COOH CHzOOOH NH m as 3 t U Table III-Continued Compound N o. Structure Stabilizer) H C S CH3 S-l5 CNHC O CI'IzN O Ha3 X- H C N H3 NNI-I\ CIIH: 8-46 /CNHCO CH2Il I C nHaa X NN CH3 S-47 CHNH (1H1 I CNHC O CH2N+C I-I X- NN CH E S-48 H (|:=(lJI-ICHz-N C 5H;a

N NH CH S s-49 ("3H3 ONHC O CHzITl C @Haa X CI'I;

8-: C 2H25-CI'ICOOH (I) O OH I IIIC 0 0 31137 5-52 C O 0 II NH O 0 0131127 5-53 CmHzsOSOaNB.

5-54 C aHa7OSOaNa GENERAL PROCEDURE AND DIRECTIONS FOR PREPARING POLYVINYL ALCOHOL SILVER HALIDE EMULSIONS The following four basic types of emulsions were selected for evaluation of the cationics (C), ampholytes (A) and stabilizers (S) listed in Tables I, II and .III, respectively.

(1) Contact printing paper emulsions (2) Projection enlarging paper emulsions (3) Ammonia type emulsions (4) Negative boiled type emulsions Detailed directions for preparing each type of emulsion are presented elsewhere in the application.

The emulsion making procedures are similar to those used for the preparation of gelatin emulsions, and employ accepted principles of physical and chemical ripening familiar to those skilled in the art. Briefly, silver nitrate solution is added to alkali halides dissolved in aqueous polyvinyl alcohol, and the resulting silver halide dispersion is subjected to a chemical ripening whereby the silver halide grains acquire their optimum light-sensitivity. Stabilizers and antifoggants may be added prior to the silver halide precipitation or during or after the subsequent chemical ripening stage. The finished emulsion is coated on a suitable support and then exposed and processed in the conventional manner.

To ensure that optimum results will be obtained from utilization of the synthetic additives described herein, a detailed account of the various factors which influence the characteristics of polyvinyl alcohol emulsions is presented. Wherever possible, and for purposes of illustration, comparsions are made with the techniques used in the gelatin emulsion system.

(1 Source of Polyvinyl Alcohol The polyvinyl alcohol, used in the preparation of the photographic emulsions described herein, is a medium viscosity type produced by the acid hyrdolysis of polyvinyl acetate. Such materials are available on the commercial chemical market and are manufactured under a variety of trade names. As examples of commercial polyvinyl alcohol suitable for practicing this invention, mention is made of Elvanol -25 sold by the E. I. du Pont de Nemours & Company and Gelvatol 2/75 available from the Shawnigan Resins Corporation, PO. Box 1531, Springfield 2, Mass.

Although synthetic polymeric silver halide carriers are not subject to variations in photographic properties to the extent of a natural substance such as gelatin, slight differences in photographic activity of various batches of polyvinyl alcohol, as purchased, may occur. In such cases, it may be necessary to make minor adjustments in the concentrations of the ampholytic and/or cationic agents.

(2) Quantity of Polyvinyl Alcohols In the preparation of most gelatin-silver halide emulsions, it is common practice to carry out the physical or Ostwald ripening (grain growth) in a small proportion of the required gelatin and to add the major quantity of the gelatin at some later stage of the emulsion making opera tion. It is well-known in the photographic art that the gelatin plays an important role in the physical ripening process and by its proper selection and use, it is possible to control the size and distribution of the silver halide grains.

Polyvinyl alcohol, on the other hand, is not as good a protecitve colloid as gelatin and it is essential to use most or all of the required polyvinyl alcohol in the physical ripening stage.

It will be noted in the formulae, which will be described later, that approximately .150 to 200.0 g. of a 12.0 to 15.0% aqueous solution of polyvinyl alcohol is needed to suspend the silver halide grains which are derived from 10.0 g. of silver nitrate. If the quantity of polyvinyl alcohol is reduced below 50.0 g. per 10.0 g. of silver nitrate, sedimentation of the silver halide grains usually occurs.

As previously stated, the ampholytic/cation combinations, as herein disclosed, increase the silver halide carrying capacity of polyvinyl alcohol. For example, Without the synthetic additives, it is possible to disperse in 150.0 g.

of 12% polyvinyl alcohol, the silver chloride derived from (3) Selection of S urface-A ctive Ampholytes and C ationics In general, the ampholytes serve as the primary means of regulating the electrical charge arrangement on the silver halide grains which ultimately determines the physical and chemical ripening response of the polyvinyl alcohol emulsions. In some instances, it may be necessary to supplement the ampholytes with one or more of the cationics in order to obtain certain photographic properties which cannot be affected with the ampholytes alone. However, the cationics, by themselves, produce very foggy emulsions unless large quantities of stabilizers and antifoggants are used in conjunction therewith in which case the emulsions are very slow and useful only for printing paper applications.

I have discovered that surface-active betaines containing quaternary ammonium and carboxylic acid groups possess excellent peptizing and physical ripening properties and are recommended for preparing all types of emulsions. The alpha betaines, in which one carbon atom separates the quaternary nitrogen and carboxylic acid functional groups, are especially applicable for the exterme speed emulsions, whereas the other members of the series, beta, gamma, delta, etc. betaines, are more suitable for the slow negative emulsions.

The surface-active amino acids listed in Table II, since they are not as efiiciently activating (grain growth, peptizing and sensitizing) agents as the betaines, are recommended for preparing positive type and paper emulsions.

The surface-active betaines and cationics possessing one or more amide linkages as a part of their molecular structure can be usually applied over a relatively broad concentration range, a property which permits a wide latitude in emulsion making conditions. Since they have low peptizing properties, the alpha betaines of this class must, in order to realize their optimum activating characteristics, be used in combination with the cationics.

The optimum concentration of the ampholytic/ cationic combinations should be determined empirically for each type of emulsion. If the concentration of the additives is too low, sedimentation of the silver halide grains will occur; and if the concentration is too high, the fog level of the emulsion will be excessive. Generally, the low speed, fine grain emulsions require a higher concentration of the ampholytic/cationics than do the high speed, coarse grained emulsions. Also, a wider cationic concentration range is permissible in the former than in the latter. For example:

Paper emulsion formulation #1 (refer to examples):

H Ampholyte A-80z C iaHai C O NIT-(CH2) 3--I I+OHZO O O- (0.01 M), 10.0 ce.

(0.01 M), 10.0 ce.

High speed formulation ta (refer to examples):

Ampholyte: Structure above (0.01 M), 10.0 cc. Catonic: Structure above (0.01 M), 0.3 cc. to 0.6 cc.

Again, it should be emphasized that the low speed emulsions are more highly stabilized with the synthetic fog inhibitors than the high speed emulsions, and can consequently tolerate a higher concentration of the cationics.

Some of the ampholytic materials are excellent peptizing and physical and chemical ripening agents, by themselves, e.g.,

5 C sHs7N -(C Hz) r-C 00 n=1, 2, 3, etc.

11:1, 2, 3, etc.

and must be utilized in a specified concentration range to achieve the desired photographic emulsion characteristics.

On the other hand, as stated above, the amide containing alpha betaines, e. g.,

peptize rather poorly, per se, even at a very high concentration level (up to 50.0 cc. of 0.01 M solution/10.0 g. of silver nitrate), and they must be combined with the as surface-active cationics listed in Table I to ensure that the silver halide grains will be dispersed satisfactorily. In the latter case, the ampholyte concentration range is not too critical, but the cationics must be used in a very narrow specified range. It should be noted that, when they are used in the high speed formulations, neither class of compounds is effective, alone.

In some instances, it is desirable to intentionally use a good peptizing ampholyte such as i C 1aH3 ITI+C H20 0 0 in a concentration range below which it alone will adequately peptize the grains, and to arrive at the desired physical and chemical emulsion characteristics by the supplemental addition of an appropriate amount of the surface-active cationics.

In the high speed boiled type emulsions, maximum grain growth is usually obtained when the concentration of the ampholytes and/or cationics is just suiiicient for proper peptization of the grains. Beyond this critical amount, the grains become progressively finer and the fog level increases proportionately. Again, it should be mentioned that the fog can be controlled by the addition of the antifoggants and stabilizers which are listed in Table III.

In the lower limits of the ampholytic/cationic concentration range, the grains possess a very broad distribution which is characterized by an emulsion possessing a. high toe speed and flat gradation. The upper concentration limit produces emulsions of a smaller average grain size, but of somewhat narrower distribution; consequently, the characteristic curve exhibits a lower speed and steeper gradation. It is to be noted that a similar relationship between the gelatin concentration and the physical (0st Wald) ripening properties exists in the boiled type gelatin emulsion system. It is well-known, to those skilled in the art, that the largest grain sizes are produced when the gelatin concentration is reduced to a value which is near the minimum amount required for peptization of the grains.

Most of the surface-active ampholytic and cationic materials are useful for the purposes disclosed in this invention when the unbroken hydrophobic chain length varies from approximately 8 to 18 carbon atoms. Below C adequate peptization of the grains cannot usually be obtained. In general, the compounds possessing the longer chain lengths (C to C are more eifective than those provided with the shorter chain radicals (C to C and they may be utilized in smaller amounts. The shorter chain compounds, on the other hand, permit a broader and less critical control of the emulsion making operations.

(4) Blending of Components It is standard practice, in working with the gelatin emulsion system, to select and blend suitable gelatins for specific types of emulsions. This technique can be applied to the polyvinyl alcohol emulsion system when the desired emulsion characteristics cannot be obtained by the incorporation of single additives. The blend may be composed of one or more ampholytes, one or more cationics, or a combination of both. The emulsions, except where indicated below, usually acquire characteristics which lay somewhere between the properties produced by the individual additives acting alone. For example:

In the above pairs, each of the individual compounds are peptizing agents in their own right. However, in the example,

All of the unwashed silver chloride emulsions are prepared with a slight excess of chloride ions, e.g., 4.0 g. of

sodium chloride per 10.0 g. of sliver nitrate.

The unwashed projection printing paper emulsions are prepared with slightly less than the stoichiometric quantity of potassium bromide (6.5 g. of potassium bromide per 10.0 g. of silver nitrate) and a slight excess of sodium chloride (0.45 g. of sodium chloride per 10.0 g. of silver nitrate).

The high speed washed emulsions may contain a considerable excess of potassium bromide (7.5 g. to 10.0 g. of potassium bromide) to facilitate the growth of large grains. This grain growth promoting method is also used in the gelatin emulsion system.

The amount of iodide may be varied from 0.05 g. of potassium iodide per 10.0 g. of silver nitrate in the paper emulsions to as high as 1.5 g. of potassium iodide per 10.0 g. of silver nitrate in the super speed emulsions. Generally, as in the gelatin emulsion system, the high iodide emulsions are faster in speed, flatter in gradation and possess a lower fog density than the corresopnding low iodide emulsions. The amount of surafcc-active cationic material must be increased in proportion to the iodide content.

(6) Percolation Variations In the gelatin emulsion system, it is standard practice to obtain the desired grain size and distribution by varying the rate of silver nitrate addition and/r dividing and adding the silver nitrate in several portions. This technique is likewise applicable to the polyvinyl alcohol emulsion system, although the response may be as great as with the gelatin emulsions. It should be emphasized, however, that it is important to select the appropriate components for the specific type of emulsions desired, and to use percolation variations chiefly for producing the minor changes in emulsion characteristics.

(7) Ripening Temperatures All the emulsions disclosed in this application may be prepared in the temperature range from 30 C. to 90 C., the lower temperatures producing the finer grain sizes, and the higher temperatures, the coarser grains. The contact and projection printing paper emulsions may be physically ripening in the 30 to 50 C. range, whereas as the negative speed emulsions are best prepared at temperatures of 60 C. or higher.

The chemical ripening phase of the emulsion making operation is carried out at 50 C. for a period of 30 minutes to 1.0 hour.

(8) Rate of Agitation The equipment in which the polyvinyl alcohol emulsions are prepared comprises stainless steel vessels which 40 have been provided with a mechanical stirring device rotating at 200.0 rpm.

Trial runs have indicated that a variation in stirring rate will alfect the emulsion characteristics. A slow rate of agitation favors the formation of larger grains, and produces emulsions which are faster in speed, flatter in gradation, and higher in fog density than when a faster rate is used.

The rate of agitation was found to be of considerable importance during the preparation of silver chloride emulsions from which the ampholytic/ cationic activating agents were omitted. It was observed that, if the rate of stirring was reduced to 25.0 r.p.m. during the silver nitrate addition, and then increased to its normal rate of 200.0 r.p.m. after a prescribed pause period, it was possible to obtain an increase in emulsion speed. The emulsion sensitivity and fog level increased in proportion to the duration of the pause. The observed behavior is probably due to the fact that a slight excess of Ag+ ions is maintained momentarily in the emulsion during the slow rate of agitation. A positive charge is thus produced on the grain surface which causes a grain growth in the silver halide.

(9) Washing of Polyvinyl Alcohol Emulsions In the gelatin emulsion system, the removal of unwanted salts can be accomplished by two general methods:

(a) The emulsion is cooled, gelled, shredded, and washed in running water to a specified conductivity.

(b) The liquid emulsion is precipitated with inorganic salts, and the emulsion particles are washed by decantation.

Polyvinyl alcohol does not form a thermoreversible gel like gelatin, and consequently it is essential to use precipitation method (b) as one of the means of removing the soluble salts.

it is known in the art that polyvinyl alcohol emulsions can be temporarily insolubilized by precipitation with certain inorganic salts such as sodium or ammonium sulfate and can then be subjected to a wash treatment. The size and hardness of the precipitated particle depends on the type, concentration, and temperature of the precipitating solution, and on the rate atwhich it is added to the polyvinyl alcohol emulsion. Ammonium sulfate produces a tougher precipitate than does sodium sulfate; whereas, mixtures of the two reagents produce particles of intermediate hardness. If the emulsion is agitated slowly during the insolubilization treatment, it is transformed into a gelatinous mass which must be torn apart and shredded by hand before it can be Washed. Small particles can usually be obtained by:

(a) Diluting the emulsion with water before precipitation,

(12) Decreasing the rate of addition of the precipitating solution,

(c) Increasing the rate of agitation, and by (d) Decreasing the temperature of the emulsion before precipitation.

Polyvinyl alcohol emulsions, which are precipitated in hard particles, withstand a vigorous wash treatment over a period of several hours, but, as a rule, become overwashed on the'surface without being washed adequately in the center of the particle. On the other hand, emulsions which are precipitated in the form of soft particles become partially solubilized before the water soluble salts are removed completely.

The precipitation of the polyvinyl alcohol emulsions is carried out, in practice, by adding one of the following solutions to the high speed formulations described subsequently.

(a) Sodium sulfate (20.0% 350.0 cc.

(b) Ammonium sulfate (40.0% 200.0 cc.

(c) Mixtures of (a) and (b). 

1. A PHOTOGRAPHIC POLYVINYL ALCOHOL LIGHT-SENSITIVE SILVER HALIDE EMULSION PRODUCED BY PRECIPITATING AND RIPENING THE SILVER HALIDE GRAINS IN POLYVINYL ALCOHOL CONTAINING A SENSITIZING QUANTITY OF AT LEAST TWO SURFACE ACTIVE AGENTS, BOTH HAVING AN ALIPHATIC CHAIN OF FROM 8 TO 18 CARBON ATOMS, ONE OF SAID SURFACE ACTIVE AGENTS BEING SELECTED FROM THE CLASS CONSISTING OF CATIONIC SURFACE ACTIVE AGENTS HAVING A FUNCTIONAL GROUPING OF THE CLASS CONSISTING OF PRIMARY AMINO (-NH2), SECONDARY AMINO (>NH), TERTIARY AMINO 